This invention relates to a catadioptric lens barrel structure including an alignment structure and a method for aligning two planar surfaces. More particularly, the present invention relates to a kinematic alignment structure using positioning knobs.
A lens barrel is a tubular mechanical structure containing a series of lenses which are aligned to transfer an image from one end face of the lens barrel to the other. Light enters one end face of the lens barrel and exits through the other. A conventional catadioptric lens barrel, as schematically shown in FIG. 1, is another type of lens barrel. The catadioptric lens barrel structure may comprise a pair of parallel lens barrels B1 and B2, and a connecting lens barrel B3 between lens barrels B1 and B2. First lens barrel B1 has an optical axis 104 running across its length. Likewise, second lens barrel B2 has an optical axis 114 running across its length. Connecting lens barrel B3 may be positioned transversely to lens barrels B1 and B2 to form either a U-configuration or, as illustrated in FIG. 1, an inverted U-configuration. In either configuration, connecting lens barrel B3 normally carries a pair of mirrors 124 and 126 to reflect the light from the first lens barrel B1 to enter the second lens barrel B2. First mirror 124 has a center point C1, while second mirror 126 has a center point C2. First and second center points C1 and C2 are located along first and second optical axes 104 and 114. Optical axis 164 connecting between first and second center points C1 and C2, respectively, is substantially perpendicular to both optical axes 104 and 114.
An optical system, such as the one illustrated in FIG. 1, may be used, for example, in a projection exposure apparatus for production of semiconductor wafers. The projection exposure apparatus includes a template positioned near an entrance end of first lens barrel B1 and a semiconductor wafer positioned near an exit end of second lens barrel B2. The projection exposure apparatus shines light through the template, photographically reduces a pattern on the template, and sequentially transfers the pattern, through first lens barrel B1, connecting lens barrel B3, and second lens barrel B2, and onto a predetermined area on the semiconductor wafer.
In semiconductor wafer production, the focus depth of the optical system is proportional to the miniaturization of a circuit pattern. In addition, mirrors 124 and 126 in connecting lens barrel B3 oftentimes do not align properly. For instance, mirrors 124 and 126 may not accurately align perpendicular to each other. Moreover, the lens barrel structure may need to be repeatedly disassembled to replace the parts or for maintenance reasons, thus altering alignment. Therefore, a primary consideration for this type of optical barrel structure includes designing components which are capable of holding high tolerances and accurate alignment. The components also need to be stable and the aligning process repeatable.
In light of the foregoing, there is a need for a kinematic alignment structure for positioning and aligning mirrors 124 and 126 in the connecting lens barrel B3, as well as an aligning method thereof.
The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purposes of the invention will be realized and attained by the elements and combinations particularly pointed out in the appended claims.
To attain the advantages and in accordance with the purposes of the invention, as embodied and broadly described herein, the invention is directed to a kinematic alignment structure. The alignment structure positions and aligns a mirror in a lens barrel. The alignment structure comprises a set of at least three positioning knobs. The positioning knobs are distributed at predetermined locations around a perimeter of an end face of the lens barrel. The mirror is positioned in direct contact with the lens barrel via the positioning knobs. The alignment structure may also comprise a cell for supporting the mirror. The cell is positioned in direct contact with the lens barrel via the positioning knobs.
A second aspect of the invention is directed to a lens barrel structure comprising a plurality of lens barrels aligned in a parallel orientation, at least one transverse lens barrel connecting two consecutive lens barrels in the parallel orientation, a support structure to support the plurality of lens barrels and the at least one transverse lens barrel, and a kinematic alignment structure for positioning a first surface and a second surface in the transverse lens barrel.
A third aspect of the invention is directed to a method for kinematically positioning and aligning a first mirror on a first end face of a lens barrel with respect to a second mirror on a second end face of the lens barrel. The method comprises the steps of providing a first set of at least three positioning knobs distributed on the first end face of the lens barrel around a perimeter thereof, and providing a second set of at least three positioning knobs distributed on the second end face of the lens barrel around a perimeter thereof. The method also involve the steps of positioning the first mirror onto the first end face of the lens barrel, and positioning the second mirror onto the second end face of the lens barrel. Then, the method involves the steps of measuring the distance and the angle between the first and the second mirrors, and polishing certain portions of the first set of positioning knobs to adjust the distance and angle of the first mirror with respect to the second mirror. The steps of positioning, measuring, and polishing may be repeated until the distance and the angle of the mirrors are within a targeted tolerance. The method may also comprise a step of providing a first cell for supporting the first mirror and providing a second cell for holding the second mirror. The first cell is positioned in direct contact with the first end face of the lens barrel via the first set of positioning knobs, and the second cell is positioned in direct contact with the second end face of the lens barrel via the second set of positioning knobs.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
Additional advantages will be set forth in the description which follows, and in part will be understood from the description, or may be learned by practice of the invention. The objects and advantages may be obtained by means of the combinations set forth in the attached claims.